The instant invention relates to a double-belt draw frame for spinning plant machines with a fiber bundling zone which follows the pair of output rollers of the main drafting zone and is followed by the pair of delivery rollers. In this known type of draw frame (DE-A1-41 39 067) an additional pair of small belts running around the pair of output rollers is installed and guides the fiber composite emerging from the pair of output rollers directly into the pair of delivery rollers and whose small under-belts run over the lower rollers of the pair of output rollers as well as of the pair of delivery rollers. The upper roller of the pair of delivery rollers is provided with suction openings arranged in ring form. In this manner a greater number of fibers are to be bundled and compacted than in known draw frames, so that almost all the fibers are brought together and are compacted in the pair of delivery rollers, thus avoiding the formation of any so-called spinning triangle.
It has been shown that this device provides only limited satisfaction. Due to the fact that the pair of output rollers is surrounded on both side by a small belt, very high pressures must be applied in order to attain a perfect drafting nip point. This is in turn a disadvantage with small belts running at high speed because these belts are subjected to greater wear due to the high stress. Additionally, the fibers are also gathered together and bundled imperfectly. It was found that the double-belt guidance of the fiber sliver emerging from the pair of output rollers causes a gathering together and bundling to take place only directly in the input nip of the pair of delivery rollers through the suction zone of the upper roller of the pair of delivery rollers. Since the fibers are deflected very much in this gathering together, they follow this deflection only in part, and this results in incomplete bundling. Furthermore, no tension drafting is possible with the known device because the small under-belts extend over the output roller and the delivery roller.
It is known from DE-39 27 936 C1 that a completely drafted fiber sliver can be gathered together in a fiber bundling zone following drafting. At the output of the draw frame, a deflection path is provided for this and is formed by the lower output roller. In the area between the nip and the following pressure rollers which are also interacting with this output roller, the output roller is provided with a suction zone for the drafted fiber roving in the vicinity of which a blowing apparatus with a flow component perpendicular to the suction zone is installed. Fiber bundling is effected by this blown air stream while the suction zone only has the task of removing the blown air. It has been shown that the deflection as well as the blown air has a negative influence on the fibers during bundling, so that the desired, improved yarn values are not obtained.